Are you talking about travel writing, writing for websites or writing for magazines? It really varies. For magazines, sometimes there are directories in professional groups (such as ASJA or Freelance Success), or paid sites like MediaBistro or Writer's Market (which is also a book). There's even a tumblr called Who Pays Writers? (http://whopays.tumblr.com/) Writer's Market also has a chart of going rates for various projects, though I think what they say for copywriting is a little low. If you're working individually with a site, I wouldn't go any lower than $1/word or $100/hour. In general, it's a good idea to keep track of your hours so you can begin to calculate pay per hour, though. A magazine that pays 50 cents a word but is easy to work with may have a higher hourly rate than a site which pays $1.50/word but requests a lot of interviews and research and/or multiple rewrites/revisions.